ml4803cs-2 Microsemi Corporation, ml4803cs-2 Datasheet - Page 8

• Manufacturer Part Number: ml4803cs-2
• Description: 8-pin Controller Combo
• Manufacturer: Microsemi Corporation

ML4803
TYPICAL APPLICATIONS
INTERNAL VOLTAGE RAMP
The internal ramp current source is programmed by way of
the VEAO pin voltage. Figure 7 displays the internal ramp
current vs. the VEAO voltage. This current source is used
8
V EAO +
ML4803
R
R
C
C
COMP
COMP
ZERO
ZERO
–
100
150
200
50
=
=
=
=
0
0.1
6 28 3
2
2
6 28 30
Figure 4. Voltage Control Loop
.
.
POWER
Figure 6. Voltage Loop Phase
´ ´
´ ´ ´
I OUT
STAGE
p
p
´
´
10
Hz
f
f
220µF
1
1
1
1
Hz
1
´
C
´
FREQUENCY (Hz)
COMP
R
´
330
COMPENSATION
V O
COMP
16
R LOAD
667
0.15µF
k
nF
10
W
=
=
330
0 16
11.3M
330k
(Continued)
.
15nF
Power Stage
Overall
Compensation
k
Network
m
100
W
VEAO
F
1000
ML4803
I VEAO
35µA
(3)
(4)
to develop the internal ramp by charging the internal
30pF +12/–10% capacitor. See Figures 10 and 11. The
frequency of the internal programming ramp is set
internally to 67kHz.
PFC CURRENT SENSE FILTERING
In DCM, the input current wave shaping technique used
by the ML4803 could cause the input current to run away.
In order for this technique to be able to operate properly
under DCM, the programming ramp must meet the boost
inductor current down-slope at zero amps. Assuming the
programming ramp is zero under light load, the OFF-time
will be terminated once the inductor current reaches zero.
Subsequently the PFC gate drive is initiated, eliminating
the necessary dead time needed for the DCM mode. This
forces the output to run away until the V
down the PFC. This situation is corrected by adding an
February 1999
Figure 7. Internal Ramp Current vs. V
–20
–40
–60
50
40
30
20
10
60
40
20
0
0
0.1
0
FF @ –55ºC
TYP @ –55ºC
TYP @ ROOM TEMP
TYP @ 155ºC
SS @ 155ºC
Figure 5. Voltage Loop Gain
1
1
2
FREQUENCY (Hz)
V EAO (V)
3
10
4
Power Stage
Overall Gain
Compensation
5
Network Gain
100
CC
OVP shuts
6
EAO
1000
7